Both are great, particularly Three UK which has been discussed in this forum.

I'm wondering if there are other similar SIMs out there from other EU countries. I'd also be curious about very low cost SIMs, though one of the advantages of the above SIMs is that they don't expire, which is great as a frequent traveler in Europe, so if you can, please include expiry info if you mention any non-freemium SIMs.